1. Field of the Invention
The present invention relates to the optimization of beam deflection in ultrasonic transmission/reception using a two-dimensional ultrasonic probe having, for example, ultrasonic transducers arranged in a two-dimensional matrix, a delay time for beam convergence, a weighting coefficient used in echo signal addition processing, and the like.
2. Description of the Related Art
An ultrasonic diagnostic apparatus is a medical image device which noninvasively obtains a tomogram of a soft tissue in a living body from the body surface by an ultrasonic pulse reflection method. This ultrasonic diagnostic apparatus has advantages of being smaller in size, more inexpensive, and safer because of no exposure to X-rays and the like than other medical image devices, and of being capable of blood flow imaging, and hence is widely used in a cardiac department, abdominal department, urological department, obstetrics and gynecology, and the like.
In recent ultrasonic imaging apparatuses, a real-time three-dimensional display function (three-dimensional real-time display function) has been put into practice. Techniques for this function include a technique (mechanical 4D scanning method) of using a mechanical 3D scanner which scans a three-dimensional area of a subject by mechanically scanning an electronic scanning type one-dimensional array transducer in a direction perpendicular to a scanning surface and a technique (to be referred to as a real-time 3D scanning method hereinafter) of realizing scanning on a three-dimensional area of a subject by electronic scanning operation using a two-dimensional ultrasonic probe having a two-dimensional array of transducers (see, for example, Jpn. Pat. Appln. KOKAI Publication Nos. 6-169921 and 9-313487).
The real-time 3D scanning method, in particular, has been rapidly popularized together with the introduction of a two-dimensional ultrasonic probe. As shown in FIG. 11, a two-dimensional ultrasonic probe used in this real-time 3D scanning method, which has ultrasonic transducers arranged in a two-dimensional matrix (e.g., 36 elements×48 elements=1728 elements), is formed by cutting a plurality of (e.g., three) blocks made of a ceramic piezoelectric material or the like (into 12 elements×48 elements each) so as to form ultrasonic transducer blocks BL having a plurality of ultrasonic transducers, and bonding the blocks BL to each other through adhesive layers as shown in FIG. 12. Note that a plurality of ultrasonic transducer blocks BL are bonded to each other through adhesive layers in this manner because it is difficult to cut one ceramic piezoelectric material block into, for example, 1782 elements by using any one of the current dicing techniques.
For example, the following problems arise in the conventional ultrasonic diagnostic apparatuses.
FIG. 13 is an enlarged view of the inside of the circle shown in FIG. 12, which shows an edge of each ultrasonic transducer block on the ultrasonic wave application side. As has been described above, the respective ultrasonic transducer blocks are bonded to each other through adhesive layers (not shown). As shown in FIG. 13, therefore, the ultrasonic transducer at one or two ends of each ultrasonic transducer block (in FIG. 13, the 12th, 13th, 24th, and 25th ultrasonic transducers to be referred to as “edge ultrasonic transducers” hereinafter) are bonded to the adhesive layers. For this reason, each edge ultrasonic transducer is subjected to the influence of bonding (e.g., changes in shape and the like), and has vibration characteristics (i.e., acoustic characteristics) different from those of the other type (which is not used for bonding) of ultrasonic transducers. However, the conventional system gives no consideration of the characteristic difference between edge ultrasonic transducers and the other type of ultrasonic transducers due to this bonding.
In addition, there are gaps (edge transducer gaps) due to the presence of the adhesive layers between edges of the ultrasonic transducer blocks. However, calculation of delay times and the like in ultrasonic transmission/reception in the prior art gives no consideration to such edge transducer gaps. This may therefore be a factor that causes a corresponding error. For example, this causes a sidelobe S like that shown in FIG. 14.